1. Field of the Invention
The present invention relates to an indoor illuminating lamp lens for a motor vehicle, and more particularly to a metal mold forming method for an indoor illuminating lamp lens for a motor vehicle and an indoor illuminating lamp lens in which a dimension is easily controlled and there is no fear that scars are left on a ceiling.
2. Description of the Related Art
An indoor illuminating lamp for a motor vehicle including a lens, a housing, a ceiling and a lamp unit is usually known in which the housing having the lamp unit to which the lens is attached is attached to a reinforcement through the ceiling (see JP-A-2005-238966).
FIGS. 6(A) and 6(B) are perspective views for explaining an indoor illuminating lamp for a motor vehicle to which the present invention is applied. FIG. 6(A) is an exploded view and FIG. 6(B) is a view of an assembled state in which an attachment is completed.
In FIG. 6(A), the indoor illuminating lamp is formed by a lens 10, a housing 20, a ceiling 30 and a lamp unit in order from an upper part.
Now, these components will be briefly described below.
<Lens 10>
The lens 10 is a resin member having a function of a lens for passing lights from a lamp 40L of the lamp unit 40 fixed to the housing 20. The lens 10 has a rectangular shape gently curved in one direction in the form of a barrel and ribs 10B (FIG. 1(B)) standing upright over 360° of the periphery of a back side thereof. In the vicinity of the ribs 10B or between the ribs, lock engaging holes 10R are provided and the lock engaging holes 10R are engaged with lock pawls 20R of the housing 20.
<Housing 20>
The housing 20 is a resin member including an upright wall 20W circulated in a rectangular shape and a bottom plate 20B that closes about half of a bottom opening surrounded by the upright wall 20W. The upright wall 20W is provided with the lock pawls 20R on side surfaces which are engaged with the lock engaging holes 10R of the lens 10 and a plurality of lock pawls 20T in an extending direction of the upright wall 20W which are engaged with a plurality of lock engaging holes of a reinforcement located in the ceiling side in a vehicle. To the bottom plate 20B, the lamp unit 40 is fixed.
<Ceiling 30>
The ceiling 30 is formed with a frame shaped resin member in plan view which forms a ceiling part when an indoor illuminating lamp for a motor vehicle is attached to an upper part of the vehicle, and includes a flat bottom surface part 30P of an inner side peripheral edge of a central opening 30L, an inclined surface part 30S obliquely standing from an end of the bottom surface part 30P and a top surface part 30T extending horizontally from a top part of the inclined surface part 30S.
<Lamp Unit 40>
The lamp unit 40 has the lamp 40L and is turned on by a signal from the vehicle. The lamp unit 40 is fixed to the bottom plate 20B of the housing 20 so that the lamp 40L protrudes from the bottom plate 20B.
<Attachment of Indoor illuminating Lamp>
In attaching the above-described components to the vehicle, initially, the lock pawls 20R of the housing 20 are engaged with the lock engaging holes 10R of the lens 10 (FIG. 6(A)) to attach the lens 10 to the housing 20. Then, the housing 20 is attached to the lamp unit 40 through the ceiling 30. Thus, the indoor illuminating lamp 1 for the motor vehicle is completed as shown in FIG. 6(B).
Then, the lock pawls 20T of the housing 20 of the indoor illuminating lamp 1 for the motor vehicle are engaged with the lock engaging holes of the reinforcement of the vehicle to attach the indoor illuminating lamp 1 for the motor vehicle to the vehicle.
<Usual Forming Method of Lens>
FIGS. 7(A)(1), 7(A)(2), 7(B), 7(C)(1), and 7(C)(2) are perspective view of a usual forming method of a lens. FIG. 7(A)(1) is a perspective view of the lens seen from a front side. FIG. 7(A)(2) is a perspective view of the lens seen from a back side. FIG. 7(B) is a perspective view showing a state that a molten resin is injected into a metal mold from a gate. FIG. 7(C)(1) shows the lens before the gate attached to the molded lens is cut by a nipper. FIG. 7(C) (2) shows the lens after the gate is cut by the nipper.
The lens 100 formed by the usual forming method is a rectangular resin member curved gently in one direction in the form of a barrel as shown in FIG. 7(A)(1). When the lens 100 is seen from the back side, such a gate mark as surrounded by a round mark F shown in FIG. 7(A)(2) is formed. FIG. 7(C)(2) is an enlarged view of the round mark F of FIG. 7(A)(2) to show that the gate mark 500K is formed. A reason why the gate mark 500K is formed and problems caused from the gate mark will be described below.
(Reason Why Gate Mark is Formed)
In order to injection mold the lens 100 as shown in FIGS. 7(A) and 7(B), initially, a metal mold is manufactured which has a cavity with the form of the lens 100 therein.
Then, an injection passage (a gate) 500 is formed for injecting the molten resin into the cavity of the metal mold to inject the molten resin into the cavity of the metal mold from the gate 500 in a direction shown by a void arrow mark in FIG. 7(B).
When the molten resin is injected into the cavity of the metal mold, the lens 100 and the gate 500 are solidified under a state that the lens 100 is integrally formed with the gate 500.
After the molten resin is solidified, when the lens 100 and the gate 500 are taken out from a molding machine, a molded product having the lens 100 formed integrally with the gate 500 is obtained as shown in FIG. 7(C)(1).
Thus, when a root part of the gate 500 is cut by a nipper to separate the gate 500 from the lens 100, the lens 100 with the gate mark 500K having a remainder of the gate as shown in FIG. 7(C)(2) is obtained.
<Problem of Lens 100 with Gate Mark>
As described above, in the usual lens 100, since the gate 500 shown in FIG. 7(C)(1) is cut by the nipper, the gate mark 500K shown in FIG. 7(C)(2) has a large gate emerging margin. Accordingly, the large gate emerging out margin of the gate mark 500K is greatly uneven and hardly dimensionally controlled.
Further, when the gate 500 is cut by the nipper, there is a fear that a designed surface of the lens 100 may be possibly broken.
Further, since the gate 500 is cut by the nipper, there is a possibility that a sharp configuration may be formed on a cut surface of the gate mark 500K. In the case of an entire surface lens, there is possibility that a ceiling may be possibly marred by the sharp cut surface.